A* Episode 17, Page 122

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  Gravitational waves seen! Black holes merge!Feb 12, 2016 2:36 AM PST | url | discuss | + share
Added 1 new A* page:You may not have noticed the space warp that swept through Earth and its environs on September 14th of last year, but two arrays of perpendicularly oriented, twin 4-km-long laser beams in the world's largest vacuum chambers, bouncing off mirrors suspended from a quadruple pendulum system by fused glass fibers only a few hair's-breadths thick in order to mute any vibration, even the natural vibrations of the molecules in the mirrors themselves, *did*: the signal they recorded, a simple line graph, matched the waveform predicted by Einstein's equations derived from his theory of relativity for the minute squashing and stretching of space—warping by a distance equivalent to only about 0.4% of a single proton's diameter along that whole 4 km beam—consistent with the force unleashed by two black holes of about 36 and 29 times the mass of the Sun, 1.3 billion light years from Earth, spiralling around each other 250 times a second before colliding at over half the speed of light, all in 0.2 seconds, to form a new black hole of 62 solar masses; the remaining three solar masses converted into that released force of the detected gravitational waves which, at their peak, equaled "50 times the total output power of the stars in the Universe at the time."
This was the first detection of a long-theorized binary black hole system, the first observation of a binary black hole merger, the first indication of a stellar-mass black hole of over 30 solar masses, and the first detection of gravitational waves, ripples that Einstein, in 1916, predicted would propagate outward across the universe from any such tremendous and sudden displacement of mass. He thought we would not be able to detect their extremely minute flexing of the space and time around us, but 100 years later, the twin LIGO ("Laser Interferometer Gravitational-Wave Observatory")arrays, one in Hanford, Washington, the other in Livingston, Louisiana, newly switched on after a lengthy upgrade process that saw them achieve a four-fold increase in sensitivity—they had been running, with no detections, since 2002—and not even yet due to resume their formal search for gravitational wave disturbances for four more days—did, and that detection means that we have a new way of looking at the universe, one that can, if refined and sensitive enough—more detectors around the world will improve the detection capability; the upcoming Virgo array in Italy, for instance, will provide a third detection spot, enabling triangulation of the source of detected gravitational waves, and continuing upgrades to the two LIGO arrays are expected to improve their individual detection capabilities by a further factor of 2.5 by the end of the decade—can potentially look past the light-opacity of the first 379,000 years of our universe—it took that long for the universe to cool to the point that atoms could form, reflecting rather than absorbing radiation and thus converting the universe from an opaque plasma to space through which those photons could travel, allowing them, eventually, to reach our telescopes as the oldest detectable light, cosmic microwave background radiation—all the way back to the very beginning, time zero, the Big Bang.
The measurements already taken of the merging of the new black hole open up a whole new era of black hole research, where the fundamental activity of black holes—gravitation—can be "seen" through the gravitational waves they propagate; dramatic events involving other massive bodies, such as neutron stars, may also become visible to the detectors. The readings provide yet another confirmation of at least an extremely low mass for the theoretical quantum particle of gravitation, the graviton, which, like the photon for light, is theorized to propagate across the universe at the speed of light, but without the interference—interposing dust, gas, gravity, and so forth—to which light is subject. In fact—or rather, in theory—gravitons interact with matter at such a low rate that actually detecting an individual particle is thought to be so unlikely as to be effectively impossible: even a detector with the mass of Jupiter, operating at 100% efficiency and in orbit around a neutron star, would only be expected to spot a single graviton once every 10 years. Still, the new ability to observe gravitational waves—in theory made up of many gravitons—could help us better understand what properties such a particle would have, and in so doing perhaps even help fill the gap in our major scientific theories between the very large—relativity—and the very small—quantum mechanics.
New conclusions and ideas about black holes themselves can already be drawn from the new data: scientists had not been certain that stellar-mass black holes over 30 solar masses could form, for instance, or that binary black holes actually merge, and the dynamics of black hole formation suggest that perhaps this could have occurred in a relatively rare type of low-mass galaxy with a young population of stars. Since we now know that binary black hole mergers DO occur—at least once, and shortly after the September 14th event, LIGO picked up a weaker signal that was probably also from black holes; in all, LIGO detected at least four events in its first run, from September through January; it will reactivate for a second run in the summer—theories of black hole formation that said they do not form through such events in any rate of time we can measure can be more or less discarded, which helps direct further theorizing along what should be more fruitful lines; the detection of the merger also enables scientists to start making estimates as to how often such events might take place in our area of the universe (LIGO can detect mergers up to about 4.25 billion light years away, and a warping of their 4-km-beams as small as 0.01% of a proton's diameter; also interesting to note: the LIGO detectors were listening in on a frequency capable of detecting mergers of black holes between 1 and 99 solar masses, and a combined mass of no more than 100 solar masses).
Well, for a black hole-based blog, this was super-exciting. : ) The BBC was so excited about it that they wrote at least three articles on it that I saw: here, here, and here. A reader sent me the link to The New York Times' thorough article, touching on many other details here. The actual research paper on the detection from the LIGO team, with some nifty charts and graphs showing what they saw, is here, and their draft of a yet-unpublished paper outlining the astrophysical implications of the detection is here (pdf format).
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